Determining height variations around a rotor

ABSTRACT

A method for determining and correcting for the variations in height of a rotor as it wobbles when rotating past a particular critical circumferential position. The method comprises sensing a reference surface of each vessel in the rotor that is to be filled during the use of the rotor in an incubator, as a tare height of the vessel, so that the effect of the vertical run-out is known and corrected for by the computer. Air pressure is used to detect the reference surface, either from a vessel-wash probe connected to the source of air pressure, or a separate sensor probe.

FIELD OF THE INVENTION

This invention relates to a method and apparatus for verifying thevertical location of cup-like vessels on a rotor in an analyzer, and forthereby ascertaining the actual amount of liquid that ends up beingplaced in such containers.

BACKGROUND OF THE INVENTION

It is known in wet assay analyzers, to determine the volume of liquid ina container by calculating the bottom height of an empty container froma reference surface, filling the container, sensing the height of theliquid-air interface of the filled container, and calculating the volumefrom the differences in height. This is taught, for example, in U.S.Pat. No. 5,443,791, column 8, lines 44-47, wherein non-contactcapacitance sensing is used. However, in this case a gauge block 24 "inone corner of the work area", column 9, lines 3-4, is the basis for an apriori assignment of the height of the bottom of the empty container.Lines 11-14 state that all stations are accurately registered withrespect to the work surface and gauge block, allowing an assumption tobe made that the height of the bottom of the empty container nevervaries.

In systems using rotors to mount the containers, the aforesaidassumption may turn out to be invalid. Indeed, in twin rotor incubatorssuch as those taught for the analyzers of U.S. Pat. No. 5,244,633,extensive vertical run-out can occur so that the height of the bottom ofan empty container can easily vary, container to container, even if thatheight is sensed at a singular fixed circumferential position passed bythe rotor. Hence, in such a case, merely sensing the height of theliquid after the container is filled, gives no assurance of the volumeof the liquid. Such volumes become important in certain assays, such asthose that have a wash and soak cycle requiring an accurate and smallvolume of wash liquid. If the error allowed in such soak volumes isonly±10 μL out of 230 μL, it is easily possible for the rotor verticalrun-out to create an error of as much as±5 μL, which is 50% of theallowed error. The smaller the volume that is used, the smaller theerror volumes that are possible. This use of 50% of the allowed errorleaves too little error tolerance for other factors in the analyzer.

There has been a need, therefore, prior to this invention, to ascertainempty and full heights of each container on a rotor, independently ofany fixed reference site not associated with the rotor. Particularlythis has been a need when operating with small volumes of liquid whichin turn are preferred for reduction in overall costs.

RELATED APPLICATION

A related application, co-filed herewith by the same inventors, is U.S.Ser. No. 08,748,306, entitled, "DETERMINING LIQUID VOLUMES IN CUP-LIKEVESSELS ON A ROTOR HAVING VERTICAL DEVIATIONS", Attorney Docket No.CDS0130. That application claims several divisible aspects disclosed butnot claimed herein, such as a method and apparatus for the determinationof liquid volumes in the vessels described herein.

SUMMARY OF THE INVENTION

We have constructed a method for making volumetric determinations forcontainers mounted on a rotor subject to vertical run-out.

More specifically, in accord with one aspect of the invention, there isprovided a method of verifying a vertical location of a plurality ofreaction vessels held spaced-apart in a movable support that is subjectto vertical deviations as it moves, the method comprising the steps of:

a) positioning the vessels in a plurality of spaced-apart, heldlocations in a movable support;

b) moving the support so as to position one of the vessels at a locationof a station critical to the processing of liquid added to the vessel;

c) ejecting air under pressure from a nozzle down towards a referencesurface of the vessel while moving the nozzle towards the surface;

d) while carrying out the step c), monitoring the pressure at the nozzleso as to detect any pressure build-up;

e) upon detection of pressure build-up during step d) that exceeds athreshold value, ceasing the moving of the nozzle and recording thedistance the nozzle moved as a measure of the vertical positioning ofthe vessel; and

f) repeating the steps b)-e) for each of the vessels.

Accordingly, it is an advantageous feature of the invention that theliquid volume of each container on a rotor can be accuratelyascertained, even in the presence of an unpredictable vertical run-outin the rotor.

Other advantageous features will become apparent upon reference to theDetailed Description that follows, when read in light of the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic, fragmentary isometric view of theincubator of an analyzer with which the invention is useful;

FIG. 2 is a fragmentary isometric view similar to FIG. 1, enlarged toshow more details;

FIG. 3 is a fragmentary elevational view in section of the rotor and oneembodiment of the invention;

FIG. 4 is a fragmentary elevational view similar to that of FIG. 3, butof an alternative embodiment; and

FIGS. 5 and 6 are views similar to that of FIG. 4, but of yet anotheralternative embodiment, showing the sequence of steps therefor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is described in connection with certain preferredembodiments, in which the reaction vessel is a cup, the movable supportis a rotor, the air pressure for the sensing comes from a pump, thecritical station along the rotor for vertical height determination is acup-wash station, and when the wash probe is also used as a sensingprobe, the air pressure is protected from the wash liquid by a one-wayball valve. In addition, the invention is applicable for vessels otherthan cups; movable supports of any kind susceptible to a verticalrun-out; sources of air pressure other than pumps (for example, a sourceof inexhaustible constant pressure); height sensing at critical stationsother than the cup-wash station; and combined sensor-wash probes usingone-way protective valves other than a ball valve. As noted theinvention is particularly useful when using small liquid soak volumes.As used herein, "small volume" means, no greater than about 250 μL.

Preferably, FIG. 1, the invention is used in an analyzer featuring anincubator 50 using at least one rotor 52 or 54 to support cups orvessels C therein at apertures 70, delivered from a cuvette-loadingstation 14. Most preferably, it is used with respect to the innermostrotor 54 at or adjacent to wash probe 78, as described hereinafter.Rotors 52 and 54 are driven by gears 66 and 68, respectively, aroundaxis 55, and various other steps in the analysis of the sample invessels C are performed at the other stations 74, 80, and luminometer32, all as described in detail in, e.g., U.S. Pat. No. 5,244,633, thedetails of which are expressly incorporated herein by reference.

Most preferably, rotor 54 is as shown in FIG. 2 and as described in U.S.Pat. No. 5,456,883, wherein each vessel-holding aperture 70 intersects apaired dump aperture 82 with a narrow passageway 83 connecting them.(Only one such pair is labeled, for clarity.) The details of said '883patent are also expressly incorporated herein by reference. Each pair ofapertures 70 & 82 is spaced away from the adjacent pair by a generallyhorizontal top surface 56, the utility of which will become apparent.

The problem to be overcome by the invention is the vertical run-out ofrotor 54 as it is rotated by gear 68. Such vertical run-out producesZ-axis vertical deviations, shown as double arrow 90. This verticalrun-out becomes critical at certain critical stations disposed aroundthe circumference of rotor 54, of which vessel-wash probe 78 isexemplary. As shown in FIG. 3, when a vessel C is rotated, arrow 100,into position under probe 78, the liquid already therein, includingpatient sample, is aspirated out by a pump 102, after the probe has beenlowered into the vessel, arrow 104. Thereafter, wash water is suppliedfrom reservoir 106 at least once, and a final wash is dispensed to anexcessive level "A" in a rough dispensing step. A fine adjustment isthen used in pump 102 to aspirate out to a known fixed level B,providing an accurate volume of soak liquid, e.g., 230 μL, for soakingthe reactive complexes inside the vessel C for an incubation period.

However, such accurate volume presumes that there has been zero verticalrun-out, arrow 90. Since, however, this is not the case, positioning theexterior surface 110 of probe 78 at level "B" will not ensure anaccurate predetermined soak volume, since the height of the vessel Cwhen empty is no longer predetermined.

In accordance with the invention, this is corrected by providing asensing probe and step wherein the empty or "tare" height of each vesselin the rotor, while in an aperture 70, is determined at the time ofmachine set-up, as the rotor rotates past a critical station (in thiscase, the vessel-wash station 78). This is done by sensing a referencesurface of the vessel. That reference surface comprises eitherhorizontal surface 56 immediately adjacent one or both sides of eachvessel, as shown in FIG. 3, or the bottom of the empty vessel C itselfas shown in FIG. 4 that is, a surface coincident with the vessel. Thatis, vessel-wash probe 78 is outfitted with a source of air pressure 120and a pressure transducer 122, connected via a one-way valve 124 thatallows air flow in the direction of arrow 126, but no liquid flowopposite to arrow 126 back to source 120 or transducer 122. As probe 78lowers towards surface 56, arrow 79, at a certain minimum distance fromthe surface the build-up of air will exceed a threshold value intransducer 122, indicating the presence of surface 56 at a known height,recorded in the analyzer's computer. The downward advance of probe 78ceases at this point. This technique is more fully described in, e.g.,U.S. Pat. No. 4,794,085, wherein the surface detected is a liquid. Asindicated, the height of surface 56 at either side of vessel C can beused, or an average of the two. The process is then repeated by rotatingrotor 54, arrow 100, until the next vessel C (not shown) is brought intoposition adjacent probe 78, and the tare height-sensing process is thenrepeated. This is done for all the vessels at all the apertures 70, FIG.2, in the entire annulus of rotor 54, because the amount of verticalrun-out 90 at station 78 may vary for each such aperture 70. Thecomputer, of course registers what the tare height is for each suchlocation, to adjust the depth the probe 78 must extend during vesselwashing to provide an effective location B for tip surface 110 thatgives the same volume of remaining soak liquid, regardless of thevertical run-out 90.

Alternatively, as shown in FIG. 4, probe 78 can extend down to thebottom of empty vessel C to detect the reference surface of the vessel,in a manner otherwise identical to the procedure described above forFIG. 3.

FIG. 5 illustrates several features of the invention. For one thing, asensing probe independent of vessel wash probe 78 can be used todetermine the tare height, especially of the bottom of each emptyvessel. Parts similar to those previously described bear the samereference numeral, to which the distinguishing suffix "a" is appended.It will be appreciated that this embodiment assumes the analyzerconfiguration is such that enough room is provided for the sensing probeto operate adjacent to the vessel-washing probe, by moving down into andup out of each vessel.

Thus, FIG. 5, rotor 54a carries vessels C₁, C₂, . . . C_(n) past acritical station, preferably the vessel aspirate-and-wash station usingprobe 78a, as before. However, in this case, probe 78a has no airpressure source or transducer connected to it. Instead, such areconnected in the same way (not shown) to a sensor 200, which is a simpletube, mounted for vertical movement, arrow 202, much as is mounted probe78a for vertical movement. (Preferably, both probe 78a and sensor 200also pivot out away from vertical alignment with rotor 54a, when not inuse, e.g., via conventional mechanisms such as motor 209 and anysuitable linkage, for sensor 200.) The air delivered by sensor 200,arrow 204 is sufficient to detect the tare height of the empty vesselunderneath it, for all such vessels C₁, C₂ . . . C_(n), during machineset-up, thus registering in the computer (e.g., computer 207) thevertical run-out effect for that portion of the rotor supporting thatparticular vessel. Because of the close proximity to probe 78a, anyvessel thereafter, arrow 205, can be moved so as to be washed, arrows206, e.g., vessel C₁ as shown, relying on the tare height determined bysensor 200 to cause an accurate soak volume to be left behind by probe78a.

The sensor of FIG. 5 can have an alternative, independent usage. Thatis, it is possible for probe 78a to also include its source of airpressure and transducer, as well as sensor 200. Each air pressure sourceand transducer can be either separate from the other, or the same sourceand transducer is used for both. In either case, the function of sensor200 is to provide an independent check on the performance of probe 78ain its aspiration and re-soaking of each vessel. In such a case, sensor200 need not be located anywhere near probe 78a (not shown) around therotor circumference. In such a procedure, sensor 200 determines the tareheight of each empty vessel during machine set-up, FIG. 5, as describedabove. Then, FIG. 6, after probe 78a has aspirated and left behind soakvolume Vs, the pertinent vessel (here C₁) is moved back, arrow 210 tosensor 200 which then moves down to sense the height of the liquidpresent, by sensing the air-liquid interface. The tare height originallydetermined is subtracted from the just-sensed liquid height, and theanalyzer computer converts the differences in heights to a volumemeasurement for that vessel C₁, given that the dimensions of the vesselare pre-known and pre-entered into the computer. This determined volumemeasurement is then compared with the "prescribed" volume pre-set forthe analyzer, to be certain it is within acceptable variations of thatprescribed volume. If it is not, then an error flag is created toindicate that probe 78a is not functioning properly.

The reason for using sensor 200 in such a case to determine the liquidheight, instead of probe 78a which also has that capability, is that itis not proper protocol to test the performance of an analyzer part(probe 78a) by using that very part being verified.

In all instances of the embodiments described above, the probe or sensornever contacts the surface that is to be detected, thus avoiding therisk of contamination.

The invention disclosed herein may be practiced in the absence of anyelement which is not specifically disclosed herein.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

What is claimed is:
 1. A method of verifying a vertical location of aplurality of reaction vessels held spaced-apart in a rotatable supportthat is subject to vertical deviations as it rotates, the methodcomprising the steps of:a) positioning the vessels in a plurality ofspaced-apart, held locations in such a support; b) rotating said supportso as to position one of the vessels at a location of a station criticalto the processing of liquid added to the vessel; c) ejecting air underpressure from a nozzle down towards a reference surface of the vesseladjacent to or coincident with said one vessel while moving said nozzletowards said surface; d) while carrying out said step c), monitoring thepressure at said nozzle so as to detect any pressure build-up; e) upondetection of pressure build-up during step d) that exceeds a thresholdvalue, ceasing said moving of said nozzle and recording the distancesaid nozzle moved as a measure of the vertical positioning of thevessel; and f) repeating said steps b)-e) for each of said vessels.
 2. Amethod as defined in claim 1, wherein said reference surface of thevessel is a surface of the support immediately adjacent said vessel. 3.A method as defined in claim 1, wherein said reference surface of thevessel is the bottom inside surface of the vessel when empty.
 4. Amethod as defined in claim 1, wherein said nozzle is a wash and aspiratenozzle and said station is the station of said wash and aspirate nozzle.5. A method as defined in claim 1, wherein said support is a rotatableincubator.